In an automotive engine, it is advantageous to be able to detect the presence or concentration of the various components in the exhaust gas stream. Such analysis and measurement can be used for controlling the operation of the engine, with a view toward optimizing the amounts of injected fuel and air. If the engine can be provided with an optimal composition of the fuel/air mixture during all operating conditions, the fuel consumption and the harmful emissions from the engine can be minimized. In addition to engine control, gas analysis and measurement can also play a role in the diagnosis of the automotive catalytic converter. The fuel and oxygen levels in the exhaust gas stream should generally lie within certain ranges for the optimum performance of the catalytic converter.
A variety of gases are typically present in an automotive engine exhaust stream, including, for example, oxygen, nitrogen oxide compounds (NOx), carbon monoxide, sulfur oxides (SOx), hydrogen sulfide (H2S), hydrocarbons, ammonia, hydrogen and water. Numerous products are known that are intended to analyze a stream of gas using a gas sensor device. A typical gas sensor device employs as sensor element(s) one or more chemo/electro-active materials, each of which is a material that will exhibit a change in an electrical property upon exposure to a gas.
A complicating factor in the process of analyzing and measuring the wide variety of gaseous components in a mixture such as exhaust gas is that the signal from one particular sensor element can be influenced by its exposure to gases other the gas(es) for which its signal is intended to serve as the desired analytical data. For example, a material selected as a sensor to respond to NOx, apart from detecting the presence or concentration of a nitrogen oxide compound, may also be sensitive to the presence of oxygen or a hydrocarbon. This difficulty has been addressed by simultaneously using a plurality of different types of sensor elements to generate enough data to permit separation of those signals that are accurately reflective of the presence of an analyte gas from those that are the unavoidable result of the cross-sensitivity of the different sensor elements to the total population of gases.
A gas sensor device constructed with a plurality of different sensor elements to address such problem of cross-sensitivity may, however, be subject to size limitations depending on the nature of its deployment. If the gas sensor device will be used for automotive purposes, it will be subject to very strict and demanding size limitations. Many currently known automotive gas sensors, such as that described for example in U.S. Pat. No. 5,556,526, must be small enough to pass through a circle having a diameter of no more than 100 mm, if not smaller. On-board automotive diagnostics is, however, not the only use for a gas analyzer having compact size as hand-held devices for monitoring all varieties of toxic and hazardous gaseous materials are becoming increasingly important.
When constructing a size-limited gas sensor, there is consequently an inevitable tension between the desire to utilize as many different sensor elements in the device as possible, and the need for the sensor device to meet the applicable size limitation. Each separate sensor element raises considerations of not only the space occupied by the element itself, but the location and arrangement of the conductors, connectors and cabling that carry the input and output pulses and signals necessary to operate all of the sensor elements that are contained in the sensor device. This has resulted in a need to develop components for the device, such as a gas sensitive apparatus, that enable increasing the number of sensor elements that can be used in the sensor device while maintaining the size of the device within permitted limits.
The present invention meets this need as it provides a gas sensitive apparatus for use as a component in a gas sensor device that permits the construction of a device containing a desirably high number of sensor elements and yet meeting virtually all applicable size limitations for use for automotive purposes or in other desired industrial settings. The use of the gas sensitive apparatus of this invention in a gas sensor device is, of course, not limited to the automotive industry.
One particular advantage of this invention is that it provides, in a gas sensitive apparatus, a space-saving arrangement for a large number of sensor elements, and the electrodes (such as printed electrodes) that are associated therewith. Another advantage of this invention is that it provides in a gas sensitive apparatus a space-saving arrangement for a plurality of conductors that are sufficient in number to carry pulse and signal inputs and outputs to and from the many sensor elements. By incorporating a large number of sensor elements in a compact, small-sized gas sensitive apparatus, the present invention enables the discrimination of very low concentrations of a wide variety of components in a gas mixture under conditions of virtually any size limitation. The gas sensitive apparatus is incorporated into a gas sensor device that is installed in an automotive vehicle or any other desired type of industrial equipment. These and other advantages are more particularly described below.